A fistula is generally a passageway formed between two internal organs. Forming a fistula between two blood vessels can have one or more beneficial functions. For example, the formation of a fistula between an artery and a vein may provide access to the vasculature for hemodialysis patients. Specifically, forming a fistula between an artery and a vein allows blood to flow quickly between the vessels while bypassing the capillaries. Needles, catheters, or other cannulas may then be inserted into the blood vessels near the fistula to draw blood from the circulatory system, pass it through a dialysis machine, and return it to the body. The quickened flow provided by the fistula may provide for effective hemodialysis. In a mature fistula, the flow rate through the fistula may be on the order of 300-500 ml/min, or may be on the order of 300-1500 ml/min, or more.
In other instances, a fistula may be formed between two veins to form a veno-venous fistula. Such a veno-venous fistula may be used to help treat portal venous hypertension. Specifically, cirrhosis or other liver diseases may cause increased resistance to flow through the portal veins draining from the intestine to the liver. This increased resistance may cause massive dilation of blood vessels, which may rupture spontaneously. To help prevent this undesirable outcome, a fistula may be formed between a portal vein and one of the major branches, thereby lowering venous pressure in the portal vein. As such, it may be useful to find improved ways to form a fistula between two blood vessels.